optimization: Batch event emissions for multi-hop trades

[AlAfiz]

Description

When a user executes a 3-hop trade (e.g., Asset A -> Asset B -> Asset C), our current logic emits a separate SwapEvent for every single hop.
Publishing multiple events to the Stellar ledger in a single transaction burns unnecessary gas and forces our indexer to reconstruct the final trade manually.
We need to aggregate the overall input and final output into a single, unified MultiHopSwap event.
This saves users money on ledger rent and simplifies our backend data architecture.

Requirements

• Define a new event topic Symbol("MultiHopSwap").
• In the swap_exact_tokens_for_tokens function, track the initial amount_in and the final amount_out.
• Publish a single event at the very end of the routing loop instead of inside the loop.
• Ensure the event payload includes the full Vec<Address> path that the trade took.

[haanarrh]

@haanarrh has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @haanarrh to this issue.

[drips-wave]

Congratulations, @haanarrh! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @haanarrh: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊